Celebrity outdoes returning long-distance traveller (8)
I believe the answer is:
spaceman
'long-distance traveller' is the definition.
'celebrity outdoes returning' is the wordplay.
'celebrity' becomes 'name' (I've seen this before).
'outdoes' becomes 'caps'.
'returning' says the letters should be written backwards.
'name'+'caps'='namecaps'
'namecaps' in reverse letter order is 'SPACEMAN'.
(Other definitions for spaceman that I've seen before include "Astronaut" , "Out-of-this-world chap?" , "High flier" , "Armstrong, say" , "one requiring a supply of oxygen?" .)